I dont fully understand about Recalculate normals
The normal of a face is the blue line, starting from the center of the face and pointing as much orthogonal as possible away from a face: it can point in two directions: one side of the face or the other.
Two connected faces, if they stay onto two different planes, can be considered as part of a &quot;sphere&quot;. Normals are calculated  outside or inside the volume of that ipothetical sphere.
In the case of more than two faces the calculation is repeated, guessing wich is the part to be considered &quot;inside&quot; and which one &quot;outside&quot;, even when the &quot;Volume&quot; is not closed (as with the two faces example).